1. Field of the Invention
The present invention relates to a prosthetic device used in the repair of atrial septal defects. More particularly, it relates to a prosthetic device which will be brought in an percutaneous and transvascular manner through a catheter and up to a defective opening of a septum present between the right and left atria.
2. Prior Art
In 1976, King and Mills reported their treatment of an atrial septal defect [JAMA, 235, 2506 (1976)]. In this first successful case wherein a prosthetic device was brought through a catheter up to the septum in an percutaneous-transvascular manner, they used a pair of umbrella-shaped disk members which were disposed in the right atrium and left atrium, respectively. A tool employed in their operation was an assembly of a central wire and two catheters coaxially combined with one another. The disk members sandwiching the septum were fixed one to the other to close the defective opening thereof. It is noted, however, that their catheters were so large in diameter and the disk members were so stiff that this operation could not be performed on young children, particularly not preschool children. Rashkind, who had tried to provide a smaller-sized device, reported in 1977 his successful clinical procedure performed on a young child patient [Circulation, 67,711 (1983)]. He used a clogging material of the single-umbrella type having hooks. The hooks, however, were highly likely to cause a jamming of the umbrella-like material, wherein the clogging material once opened within a heart could never be displaced therein or removed therefrom. In such an event, doctors would have to perform open heart surgery. He then proposed an improved device comprising two umbrella-shaped members united integrally with each other, and this device has been widely used in the clinical treatment of the patent ductus arteriosus.
On the other hand, Lock, who had improved Rashkind's device of the double and integral disk type, added a coiled spring to an intermediate portion of each of eight stainless steel ribs. The two disks capable of tightly overlapping one another can now firmly grip a thin septum present between the atria. He has filed a patent application for his improved system (see EP 0 541 063 A2). Lock's device having the umbrella-like disks resembling as a whole a clam, viz. one species of Bivalvia, is called a "clamshell umbrella". A long sheath of the 11F type catheter is inserted into a patient's femoral vein, so that Lock's device can be used for any patient who weighs 8 Kg or more. Thus, Lock's method is virtually the first clinical success in the surgical remedy of atrial septal defect wherein percutaneous-transvascular catheters are used.
Some parts such as hinges and arms of the stainless steel ribs in Lock's umbrella were, however, found broke soon after arrangement in the patient's heart, due to metal fatigue or deterioration in strength occurring in vivo. Therefore, the clinical testing was interrupted recently in the U.S.A. and in Japan. Further, it is almost impossible for Lock's umbrella to be placed in the center of the opening in the defective septum. In order to compensate for an offset of the umbrella from the center of the opening, the former must be twice as large as the latter, increasing the length of stainless steel ribs required.